The flow cytometry core will be an integral part of the overall proposal and will provide a facility for analyses of cell samples for surface markers associated with cell activation and function for assessment of purity of cell preparations used in functional assays for monitoring cell cycle progression for measuring apoptosis, and for determining cytokine synthesis by individual cells. In addition, the core will provide capabilities for sorting phenotypically distinct populations of cells for the projects which will investigate activities of heterogeneous lymphoid preparations. the core will be located at the La Jolla Institute for Allergy and Immunology, which is in walking distance from Scripps Research Institute, and will consist of several Becton Dickinson instruments including one FACScan used for analysis only, one FACScan and FACStar can distinguish fluorescence at three wavelengths simultaneously whereas the FACScaliber is capable of four color analyses. All instruments are available at the present time. Funds are requested to support the maintenance and repair of the instruments to insure they are functional and available to investigators at all times, and for part time support of a research technicians salary. The technician will oversee the daily running of the machines and provide assistance with analysis of samples. All projects of this program will utilize this core to some extent with project 3 heavily dependent on this facility (Project 1, 15%; Project 3, 65%, Project 4, 5%). FACS analyses will be used primarily to characterize various mast cell populations generated in Project 3, and also used in Projects I and 2, for surface markers such as B7-1 and -2, ICAM- 1, CD40- and CD40L, VLA-4 and -5, and for analyzing and purifying different subsets of T cells (Projects 1 and 3). Additional uses will include assessing C3a receptor expression, actin polymerization, and apoptosis (Project 2), calcium mobilization (Project 1) and bradykinin receptor expression (Project 4).